A wind turbine used to generate power to feed into the electricity grid generally comprises a nacelle mounted on top of a tower. An aerodynamic rotor with blades mounted to a hub is generally found at the “front” of the nacelle, and the generator itself is housed inside the nacelle. To maximise the amount of energy that can be extracted from the wind, it must be possible to turn the nacelle so that the aerodynamic rotor can always face directly into the wind. To this end, the nacelle is generally mounted to the tower by means of a yaw assembly. The yaw assembly can comprise a toothed yaw ring mounted to the top of the tower. The yaw ring can be constructed so that the yaw ring teeth face outwards (to the exterior of the tower) or inwards (into the interior of the tower). The yaw assembly comprises a number of yaw motors with gear pinions that engage with the yaw ring. By appropriately controlling the yaw motors, the entire nacelle can be rotated in the desired direction and by the desired amount. The teeth of the yaw ring are subject to wear and tear. A fractured yaw ring tooth is weakened and may even break off completely. When a yaw ring is missing a tooth, the yaw gear pinion cannot mesh correctly with the yaw ring any more. As a result, the yaw gear pinion may suffer damage and may also cause further damage to the yaw ring. Another possible source of damage to the yaw ring can be foreign objects that inadvertently come between the yaw ring and a yaw drive pinion.
While it is possible to repair a damaged or broken yaw ring tooth, for example by welding a new tooth into place, or by adding a suitably shaped plate to the yaw ring to simulate a tooth, a repaired tooth or replacement plate is a relatively weak element and will never have the same strength properties as an undamaged tooth. However, the present designs do not provide for any way of avoiding loading of such a weak element. If the repaired yaw ring tooth should fail again, the yaw ring will need to be replaced. This is a very costly operation, since the entire nacelle must be detached and lifted upward (for example using a jackup crane) to allow the damaged yaw ring to be removed through the space between the tower and the raised nacelle and to allow a replacement yaw ring to be installed. This procedure is very expensive, hazardous, and time-consuming. One way of reducing the cost of such a procedure is to use a segmented yaw ring instead of a one-piece yaw ring. However, a drawback of such a segmented yaw ring is that it is often more complex than a normal one-piece yaw ring, and therefore more expensive to manufacture. There are no recognized design standards for segmented yaw rings. Furthermore, it is difficult to evaluate the influence of the transition from one segment to another. Another drawback of a segmented yaw ring design is that it requires more space. In any case, the teeth of a segmented yaw ring are just as liable to become damaged over time, and the replacement of a yaw ring segment is also associated with cost, safety risk, and effort.